The use of radar in navigation allows mapping of sectors. For example, autonomous ground vehicle navigation has used radar to produce a two-dimensional map of the terrain ahead of the vehicle. Referring to FIG. 1, a grid comprising range RA and cross-range CR dimensions to define cells such as cell C has been employed to lay out the area in front of the vehicle. The difficulty of traversing an obstacle in a cell of the grid was assumed to be proportional to the amplitude of the returned radar signal from the cell. This assumption can be impractical in certain environments because different shapes reflect radar signals differently. For example, a very small corner reflector may return a much greater amplitude signal than a very large obstacle of a different shape. Thus, the amplitude of the reflected radar signal may not be indicative of obstacle height.
Mapping techniques using laser scanning create a three-dimensional map using range, cross-range and height. The height is measured by sweeping the laser vertically with respect to an obstacle. This type of sweep used in laser scanning can be impractical in real beam radar systems and other radar systems which do not employ lasers because the radar signal in real beam systems tend to have a very wide beam which does not allow sufficient accuracy and consistency to provide useful information regarding the height of the object. Lasers systems cannot operate in low visibility conditions because they are based on a light beam, whereas radar systems of the proper design can operate in any conditions.
Interferometric synthetic aperture radar (IFSAR) has employed techniques to determine relative height of objects being mapped. However, these IFSAR techniques do not result in sufficient information to consistently provide actual height information. Also, IFSAR cannot be used on ground vehicles because it relies on doppler information integrated over time. Ground vehicle guidance does not generate sufficient Doppler information over time for integrating.
Thus, there is a need for a system and method for measuring the height of an object reflecting a real beam radar signal.